In Ubon, I will recommend The Outside Inn on the far east side of Suriat rd, Padaeng Mansion on Padaeng rd, and T3 House on Sapphasit rd.
The first is a 25 min walk away from the city park and has a restaurant with excellent Mexican food (and more) The 2 others are closer to the park, and Padaeng Mansion is right across the rd from Wrongway Cafe, the most popular farang hangout in town. They will cost around 500 baht/night.